1. Technical Field
The present invention relates to control systems for power supplies, and more particularly to an output-switch control system for an AC-DC power supply that ensure users' operational safety.
2. Description of Related Art
Referring to FIG. 1, a conventional output-switch control system for a power supply comprises a first contact switch 1 and a second contact switch 2. The first contact switch 1 is a contact switch in an open-circuit state, and the second contact switch 2 is a contact switch in a close-circuit state. In use, the first and second contact switches 1, 2 jointly send voltage signals to a detecting circuit 7 through reference voltages 3, 4 and shunt resistors 5, 6, respectively. The detecting circuit 7 has an input pin connected to the loop of the second contact switch 2, and another input pin connected to the loop of the first contact switch 1. Thereby, the system uses the voltage signals of the first and second contact switches 1, 2 to control the detecting circuit 7 to make a high-voltage switch 8 turn on its high-voltage output.
Now referring to FIG. 2, when a user presses a switch button 9 of the control system, the first contact switch 1 has its movable contact 101 coming to contact with a fixed contact 102, and thereby turns into a close-circuit state, while the second contact switch 2 has its movable contact 201 departing from the fixed contact 202, and thereby turns into an open-circuit state. Upon the foregoing state transition of the first contact switch 1 and the second contact switch 2, transition signals are sent to the detecting circuit 7 through the reference voltages 3, 4. Thereby, the system can control the detecting circuit 7 using the voltage signals of the first and second contact switches 1, 2, so as to make the detecting circuit 7 turn on the high-voltage output.
While the existing output-switch control system turns the switch on or off using the first and second contact switches 1, 2 separately, once either of the contacts has poor contact or becomes fatigued, the output-switch control system can fail to properly turn on or off the high voltage high-voltage switch 8, risking its user to electric shocks. Hence, there is a need for switch control in power supplies that ensures users' safety.